Quantum mechanical entanglement-like behaviour has been observed during the investigation of the dowsing effect. Interference fringe patterns, a hallmark of wave behaviour, have been observed when parallel copper tubes are placed on the ground. The fringes can be mapped using right angled dowsing rods. When the tubes are touched together and then replaced in their original position the fringe pattern changes in a manner that suggests that the tubes are "entangled". This change persists until "decoherence" occurs due to environmental interactions or deliberate physical actions.Polarisers that use a class of materials that have no effect on electromagnetic waves but act as polarisers for dowsing radiation are used to investigate radiation passing between the tubes. The polarisers are used both to screen from interference and to facilitate measurement of the characteristics of the radiation.Blind testing has suggested (z= 7.19, p=0.000000007%) that dowsing rods can be used to detect changes in interference fringe patterns created by the copper tubes both when they are "entangled" with one another and when they are decoherent. It has also demonstrated (z=5.2, p=0.00003%) that the radiation has a wavelength of 21.1 cm, and is circularly polarized.The use of non-conventional material for the polarisers strongly indicates that the radiation is likely not electromagnetic in nature and suggests a testable proposition that the radiation that causes the dowsing entanglement effect is one and the same as that which creates entanglement in quantum physics.